The present invention relates to an apparatus and method for installing rivets in aircraft structures and more particularly to a hand-held single impact rivet gun used for back riveting in conjunction with back bar tooling.
Structural joining processes used for aircraft airframe skin structure basically are either bonded or riveted. Aside from other engineering and manufacturing factors used for the selection of the appropriate joining process, bonded structure has superior aerodynamic qualities while riveted structure costs less to produce. A need for a joining process which is aerodynamically smooth and inexpensive as riveted structure has become a general goal in aircraft design. Devising a riveting process which can produce the smooth appearance of a bonded structure would satisfy both the esthetics, aerodynamics and manufacturing costs requirements. A riveting method to fulfill these needs is one which back drives the shank of the rivet on the inside surface of the aircraft structure so there are no protruding rivet heads on the exterior surface, while the head of the rivet is set in a countersunk hole so as to provide a flush and smooth exterior surface.
The standard riveting techniques used today involve one person holding the rivet with a bucking bar against the shank of the rivet while a second person with a rivet gun upsets the rivet on the exterior surface which sometimes deforms the sheet metal skin. Conventional rivet guns apply rapid impact strikes to the rivet head which sometimes overdrives the rivet causing a deformation to the skin. Single impact rivet guns can be accurately adjusted so the rivet is not over or under driven and there is no possibility of deforming the aircraft skin. Single impact rivet guns are obviously faster than the conventional rivet guns and have more precise control in upsetting the rivet.
The concept of a single impact rivet gun has been around for at least two decades, as illustrated in U.S. Pat. No. 4,039,034 to Wagner and U.S. Pat. No. 4,192,389 to Raman. In the first patent listed, the rivet gun is manually held while in the second patent the rivet gun is mounted in an overall structure which also holds the sections being riveted and the bucking bar on the opposite side of the rivet. Conventional riveting techniques involve a hand-held rivet gun with a bucking bar held on the opposite end of the rivet normally by a second person. The concept of back riveting, wherein the shank of the rivet is on the inside of the aircraft structure rather than the outside, is old as taught in U.S. Pat. No. 4,007,540 to Tyree and U.S. Pat. No. 2,312,554 to Jocques.
The concept of a single person riveting operation is generally old in the art, as taught by U.S. Pat. No. 2,559,248 to Harcourt, U.S. Pat. No. 4,967,947 to Sarh, U.S. Pat. No. 4,662,556 to Gidlund, and U.S. Pat. No. 4,759,109 to Mason et al. All of the last four mentioned patents teach a machine which holds the section of the aircraft being riveted as well as the backing bar device and the riveting gun in an automated unitary structure wherein the backing member moves with the rivet gun across the surface of the section being riveted. U.S. Pat. No. 2,312,554 to Jocques, previously mentioned, also teaches a single person riveting apparatus which again is a unitary structure like the above-mentioned four patents. In the above-mentioned patent to Sarh the bucking component and the riveting component are both mounted on a universal base wherein the bucking unit and the riveting unit are computer controlled for three axis movement in unison.
The concept of an offset rivet gun whereby the driving hammer for the rivet is offset from the axis of the piston and impact pin is taught in the above-mentioned patent to Jocques; however, it is not hand-held nor is it used to drive a rivet under an extending flange of a C-channel, as done in the present invention.
The rivet gun of the present invention is a hand-held pneumatic gun which back drives the rivets against a solid tooling surface having an identical shape of the aircraft section being fabricated. This process replaces the hand-held bucking bar for each rivet with a stationary tooling surface which provides a backing bar for all of the rivets within the section being fabricated.
Since the single stroke of the rivet gun is carefully limited by a stop, it upsets the shank of the rivet the precise amount necessary to swell the shank and upset the end of the shank to form a head and tightly contain the two or more sheets being joined. Driving the rivet with one controlled hit instead of several also provides a speed advantage over a traditional riveting and also greatly increases the exact amount of upset of the rivet. The sheet clamp up force can also be controlled with the present rivet gun in light of the built-in spring which requires the riveter to push the rivet gun against the rivet until the spring is fully compressed. Once the spring is fully compressed the trigger automatically unlocks and the rivet gun is armed and ready to fire. The spring compression that is generated clamps both the sheets being riveted together and reduces the possibility of a non-shear condition existing between the sheets. The actual rivet gun of the present invention is very similar to a nail gun used in house construction which performs the same basic task as a single impact rivet gun only with more stroke of the impact pin.
The principal object of the present invention is to provide a single person riveting method which utilizes a single impact rivet gun for back riveting against a fixed tooling surface.
A further object of the present invention is to provide a rivet gun having an offset driving hammer for reaching under the flange of a C-channel.
Another object of the present is to provide a single piece of stationary back bar tooling for backing all of the rivets in a section of aircraft being constructed.
Another object of the present invention is to provide a riveting technique which leaves the exterior aircraft surface smooth with no deformation of the skin and the rivets not visible.
Another object of the present invention is to provide a back riveting gun which precisely upsets all of the rivets so as to provide a maximum strength connection.
Further objects and advantages will be pointed out or will become evident in the following detailed description, claims and the accompanying drawings.